fixed test case to produce same results on txn-enabled binary. 
    temporary fix - permanent fix is it make mysqld behave the same with
    MyISAM on auto_increment insert after delete from tbl_name regardless
    of how the binary was compiled
sql/slave.cc
    fixed concurrency bug with log_seq
sql/slave.h
    last_log_seq needs to be updated atomically with pos
sql/sql_repl.cc
    cleared up comment and fixed concurrency bug


mysql-test/t/rpl_sporadic_master.test:
  fixed test case to produce same results on txn-enabled binary. 
  temporary fix - permanent fix is it make mysqld behave the same with
  MyISAM on auto_increment insert after delete from tbl_name regardless
  of how the binary was compiled
sql/slave.cc:
  fixed concurrency bug with log_seq
sql/slave.h:
  last_log_seq needs to be updated atomically with pos
sql/sql_repl.cc:
  cleared up comment and fixed concurrency bug